iPhone software update URL

Does anyone know the address for the iPhone software update site. My company's fortiguard system is blocking the site and I need the address so that my IT guys can open it up. When I click the "check for update" box all I get back is an Apple message that says the site can not be reached. This I know, but Apple's little message doesn't bother to tell me what the site is that has been blocked. Can anyone help?